The first goal of this project is to gain an understanding of the active electro-sensory system in the weakly electric mormyrid fish. We anticipate making quantitative descriptions of the current source, of current distribution, and of the response of electroreceptors during the electric organ discharge (EOD). However, the major emphasis will be on the central nervous system, particularly on the posterior lateral line lobe (PLLL) and the valvula cerebelli. Primary electroreceptor afferents terminate in PLLL. PLLL also receives input associated with the command signal. Normally the EOD follows the command signal, but this association can be broken with curare and other means. The valvula is the mormyrid gigantocerebellum. In both structures we will begin with functional anatomical and pure anatomical questions using both electrophysiological techniques and recent anatomical methods for tracing pathways. In the PLLL we will then pursue more functional questions. We will ask if the input associated with the command signal conveys information about prior input. We will also examine the response of PLLL neurons to EOD input in the presence of field distorting objects. We will attempt to understand these responses in terms of input from electroreceptors, the command input and the connectivity of PLLL. The second major goal is to determine the areas of cerebellar cortex which project onto single cerebellar nuclear cells. We will note the relationship between a cell's position in the nucleus and the position on the cortical surface of the area projecting to it. These studies will be done in the crocodillian, Caiman sclerops.